This invention relates to an arrangement for driving a rocking gripper particularly for sheet printing machines.
Arrangements for driving a rocking initial gripper have to impart to this gripper an operating motion consisting of three parts: (a) a continuous starting from a first rest position to a uniform movement at a speed coincident with the circumferential speed of the impression cylinder, (b) a continuous retardation up to the second rest position, (c) a continuous starting and retardation during return to the first rest position. In the first rest position the chucks of the initial gripper seize a previously lined up sheet and transmit it at a synchronous speed of the initial gripper and the impression cylinder to the chucks of the impression cylinder.
One of actually known arrangements for driving a rocking initial gripper is accomplished by application of a toothed segment fixed on the shaft of the initial gripper, this toothed segment meshing with a second toothed segment provided with two rollers rolling along a couple of cams.
A drawback of this arrangement is that the mutually meshing toothed segments do not secure an accuracy and uniformity of movement of the rocking initial gripper, required for maintaining a register in printing.
Another known drive of a rocking initial gripper uses for its working movement again toothed segments with the difference that the shaft of the initial gripper is supported on eccentrics, enabling an accomplishment of the movement from the second rest position to the first one along a different track.
A drawback of this arrangement is as in the earlier mentioned arrangement that it does not secure the accuracy and uniformity of movement, required for maintaining a register in printing.
A further known driving arrangement of a rocking initial gripper derives it working movement from a couple of cams, with rollers supported on a two arm lever bearing against their surfaces, the rocking motion of said lever transmitted by a rod to an arm of the initial gripper.
A drawback of this arrangement is that the necessary clearances in the joints of arms and rods cause an inaccuracy of the movement of the rocking initial gripper and thus also an inaccuracy of the maintenance of a register in printing.